It boosts their memory and makes them better pollinators, according to a study published in the journal, Science.

Honeybees fed a sugar solution containing caffeine, which exists naturally in the nectar of coffee and citrus flowers, were three times more likely to remember a flower's scent than those feeding on just sugar.

"Remembering floral traits is difficult for bees to perform at a fast pace as they fly from flower to flower and we have found that caffeine helps the bee remember where the flowers are,'' wrote Professor Geraldine Wright.

"In turn, bees that have fed on caffeine-laced nectar are laden with coffee pollen and these bees search for other coffee plants to find more nectar, leading to better pollination,'' the Newcastle University neuroethologist said.

The effect of caffeine on the bees' long-term memory was significant: three times as many bees remembered a floral scent 24 hours later and twice as many bees remembered the scent after three days.

The research team learned the nectar of certain citrus and coffee flowers often contains low doses of caffeine.

These include the robusta coffee species mainly used to produce freeze-dried coffee and the arabica used for espresso and filter coffee. Grapefruit and lemons were found to have caffeine.

"Caffeine is a defence chemical in plants and tastes bitter to many insects, including bees, so we were surprised to find it in the nectar,'' said co-author Phil Stevenson of the University of Greenwich, also in Britain.

"However, it occurs at a dose that's too low for the bees to taste but high enough to affect bee behaviour,'' he added.

"This work helps us understand the basic mechanisms of how caffeine affects our brains. What we see in bees could explain why people prefer to drink coffee when studying.''

Stevenson said: "Understanding a honeybee's habits and preferences could help find ways to reinvigorate the species to protect our farming industry and countryside.''